Posted on 05/20/2006 6:02:56 PM PDT by Al Simmons
Fetus' Feet Show Fish, Reptile Vestiges By Jennifer Viegas, Discovery News
May 18, 2006 — The feet of human embryos taking shape in the womb reveal links to prehistoric fish and reptiles, a new study finds.
Human feet may not look reptilian once babies emerge from the womb, but during development the appendages appear similar to prehistoric fish and reptiles. The finding supports the theory that mammalian feet evolved from ancient mammal-like reptiles that, in turn, evolved from fish.
It also suggests that evolution -- whether that of a species over time or the developmental course of a single organism -- follows distinct patterns.
In this case, the evolution of mammalian feet from fish fins to four-legged reptiles to four-limbed mammals to human feet appears to roughly mirror what happens to a maturing human embryo.
"Undoubtedly there are clear parallels between the mammal-like reptilian foot and the human foot," said Albert Isidro, an anthropologist at the Autonomous University of Barcelona, Spain and lead author of the study, which appeared in the journal The Foot.
Isidro and colleague Teresa Vazquez made the determination after analyzing fossils of a number of mammal-like reptiles that lived from 75 to 360 million years ago. The scientists also studied fossils of osteolepiform fish, which appear to be half fish and half reptilian. These fish lived 400 million years ago and had lungs, nostrils and four fins located where limbs would later be found in four-footed reptiles and mammals.
In 33-day-old human embryos, the scientists observed "the outline of a lower extremity in the form of a fin, similar to that seen in osteolepiform fishes." As the embryo continued to develop, the researchers focused their attention on two foot bones: the calcaneous, or heel bone, and the talus, which sits between the heel and the lower leg.
At 54 days of gestation, these two bones sit next to each other as they did within the reptile herbivore Bauria cynops, which lived around 260 million years ago. This ancient reptile had flat, crushing teeth and mammalian features.
At eight and a half weeks of gestation, the researchers found the two embryonic foot bones resemble those seen in the Diademodon vegetarian dinosaur, which lived around 230 million years ago.
"We can tell that the embryo is half way between the reptiles and the mammals (at this stage)," Isidro told Discovery News.
The two foot bones continue to develop until, at nine weeks, they resemble that of placental mammals as they emerged 80 million years ago.
This development of feet in the human embryo mirrors how the foot evolved over millions of years beginning with fish and ending with early mammals, according to the scientists.
Supporting the fish/foot link was the discovery last month of a new species, Tiktaalik roseae, which lived 375 million years ago. It had fish fins and scales, but also limb parts found in four-legged animals.
"Tiktaalik blurs the boundary between fish and land-living animals both in terms of its anatomy and its way of life," said Neil Shubin, professor and chairman of organismal biology at the University of Chicago and co-author of a related paper in the journal Nature.
H. Richard Lane, director of sedimentary geology and paleobiology at the National Science Foundation, said, "These exciting discoveries are providing fossil ‘Rosetta Stones’ for a deeper understanding of this evolutionary milestone: fish to land-roaming tetrapods (four limbed animals)."
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Just the French.
sorry, couldn't resist.
72 platypusses? Now I know all. ;) I wonder what I get?
Tie me kangaroo down, Clyde.
Mind me platypus duck, Bill,
Mind me platypus duck.
Don't let him go running amuck, Bill,
Mind me platypus duck.
All together now!
Tie me kangaroo down, sport,
Tie me kangaroo down.
Tie me kangaroo down, sport,
Tie me kangaroo down.
http://www.whatsthenumber.com/oz-u/songs/tie-me-kangaroo-down-11.htm
Your response suggests you didn't follow the thread very well. It's late at night. Saturday evening in fact. I suppose a fellow could lose his place eh?!
Thanks for the response. The Wiki gives what I had originally thought. The theory was developed in the 1860's, has been discarded, but still gets brought out, probably because people read it in a book, put it in a new book, etc. Although I'm a creationist, I don't see the discrediting of this hurting evolutionary theory in the least. Nothing of what I understand about evolution demands this process during the pre-birth phase.
After I started reading Richard Dawkins, I started getting invited to more parties and noticed there were always more girls standing around trying to get in on the conversation.
You really do gotta' read this stuff ~ you're beginning to sound like CarolinaMom anyway ~ are you folks maybe related, like brother/sister, or the Madonna and Child?
Hand me the amniocentesis equipment...
The naked eye is not a sensitive enough instrument for many measurements.
Cheers!
No doubt it's much later where you are than where I am.
LOL!
Dawkins did write some interesting books. Now can I get in on the conversation? ;o)
Lots of cool quotes:
http://www.simonyi.ox.ac.uk/dawkins/WorldOfDawkins-archive/Catalano/quotes.shtml#short
"The world becomes full of organisms that have what it takes to become ancestors. That, in a sentence, is Darwinism"...Dawkins.
"There's this thing called being so open-minded your brains drop out."
Correct. Instead you get balut.
(Warning - if you don't know what balut is and tend to be squeamish, you might not want to follow this link.)
You need to re-read these passages from the article:
An early form of the law was devised by the 19th-century Estonian zoologist Karl Ernst von Baer, who observed that embryos resemble the embryos, but not the adults, of other species.
and...
Modern theory
One can explain connections between phylogeny and ontogeny if one assumes that one species changes into another by a sequence of small modifications to its developmental program (specified by the genome). Modifications that affect early steps of this program will usually require modifications in all later steps and are therefore less likely to succeed. Most of the successful changes will thus affect the latest stages of the program, and the program will retain the earlier steps. Occasionally however, a modification of an earlier step in the program does succeed: for this reason a strict correspondence between ontogeny and phylogeny, as expressed in Ernst Haeckel's discredited recapitulation law, fails.
See? Each gene does a specific thing, is triggered by a molecule with a specific shape meeting its promoter region - and also gets turned on or off at a specific point in the organism's development.
So a mutation to a gene could affect any or all of those aspects of it. But an organism that has this new mutation to a gene will be indistinguishable from a comrade at the same age until the new mutation starts making itself felt. Add up all the mutations that distinguish one species from its parent species, and you have individuals in the new species going off on their own developmental pathway at some point in their lives - and tending to create precisely the pattern that von Baer (but not Haeckel!) predicted.
BTW, this book, Endless Forms Most Beautiful, is supposed to be an excellent book on the subject of evo-devo - the hot subfield that real, live evolutionary biologists of today work in, studying embryos. (I haven't read it yet, but it got great reviews.)
However, like anatomy, ontogeny does follow a remarkable progression when you move from species to species in the evolutionary chain...
There are some amazing facts that led Haeckel astray
My favorite is the way that mammalian ear bones start out in the jaw and then migrate to the ear. This exactly mimics the fossil progression from reptiles to mammals.
It also pretty much disproves ID because an engineer faced with the task of making a better ear would leave a perfectly good jaw joint alone and simply modify the ear.
Other examples of embryological vestigisms are the egg shell that forms around a developing marsupial embryo (and is reabsorbed before it's born), and the egg teeth that some marsupials have but never use.
Thanks for the pings!
Fascinating. So you're saying that there's no "reason" for the nerve to wrap around the heart before ending at the throat? Now that you mention it, the pulsation of fish gills do resemble the vibration of vocal cords!
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